Composite abrasive wheels are formed by adhering abrasive particles by means of an organic polymer to the fibers of a nonwoven fiber web. Multiple plies of such webs are then laminated to form a slab from which the wheels may be cut or the web may be wound spirally to form a log from which the wheels may be cut. Applications of these widely used wheels include polishing, deburring, finishing, and cleaning of metallic parts.
The surface temperature of the metallic part while being abraded by such a wheel can exceed 65.degree. C. and some parts, depending on the alloy type, can even reach a surface temperature of 120.degree. C. Therefore, the thermal properties of the organic polymer play a critical role in the performance requirements of the abrasive wheels as elevated temperatures are encountered in most applications.
Abrasive wheels with poor thermal properties often lead to undesirable "smearing" of the workpiece as a result of the contamination of the workpiece surface with melted binder. Also premature thermal degradation of the binder system reduces the useful life of the wheel. Thermal properties include softening point, melting point, glass transition point (Tg), and degradation temperature.
The most commonly used organic binder for use in composite wheels is a polyurethane such as is described for example in U.S. Pat. Nos. 2,885,276, 4,227,350 and 4,609,380.
A polyurethane has the generic structure ##STR1##
The thermal stability of polyurethane is a function of the nature of the linking groups R.sub.1 and R.sub.2, and most polyurethanes have a softening point that is relatively low.
U.S. Pat. No. 4,609,380 addresses this problem and uses a polymer blend of a polyurethane with a compatible polymer having a glass transition temperature of at least 50.degree. C. to endow the blend with a glass transition temperature of at least 40.degree. C.
In this patent the compatible polymer merely constitutes a part of the physical mixture when blended with high molecular thermoplastic polyurethanes, such as Estane resins from the B. F. Goodrich Company.
The present invention provides a different and more advantageous route to providing a binder with the required high temperature stability for optimum performance.